His reputation for holiness spread, and Cerbonius was chosen bishop of Populonia, Italy c.544; he soon became unpopular as he conducted Sunday Mass at dawn, forcing his flock to get up in the middle of the night. PopeVigilius summoned him to Rome to answer the complaints. When he arrived, Cerbonius woke the pope at dawn for Mass; the two heard the singing of angels, Vigilius gave him permission to say Mass whenever he thought proper, and sent him home.

For hiding Roman soldiers who were fleeing invading Ostrogoths, Cerbonius was ordered to be executed by being thrown to a bear. The bear was terrified of Cerbonius, fell to the ground and began licking the bishop‘s feet. Cerbonius was exiled to the island of Elba, Italy instead, where he spent the rest of his life as a prayerfulhermit.